Certain elements of manufacture require both acoustical and structural qualities in particular applications. One example of such a requirement is found in a jet engine housing for an airplane. In particular, an engine housing must function as both a noise suppressor and a structurally sound encasement of the engine therewithin disposed. This dual task now is accomplished by employing two-sheet fabrication comprising a porous first sheet or "skin" for acoustical control and a second perforated skin for structural stability. Both functions cannot be accomplished by present porous-sheet construction since normal laser-drilled or chemically-etched apertures yield sheets that are poor in structural and fatigue strength and thus require a second perforated sheet for structural capability. Specifically, apertures formed by normal laser drilling or chemical etching have rough edges and cannot be tailored to indicated geometric and size characteristics for particular applications, and the sheets so constructed experience poor fatigue life and structural integrity. Further, because of the limited quality and geometric choice of these prior-art apertures, friction-to-surface values can be relatively high which can cause clogging and resultant airflow disruption.
In view of the above considerations, it is apparent that a need is present for a metallic or non-metallic sheet having both acoustical and structural functionality, and for a process for producing such a sheet. Accordingly, a primary object of the present invention is to provide an acoustically and structurally functional porous sheet and a process for its formation.
Another object of the present invention is to provide such a sheet wherein a plurality of apertures therethrough are formed by a free-electron laser beam.
Yet another object of the invention is to provide such a sheet wherein the plurality of apertures are of a size and number sufficient to enable the sheet to function as an acoustical noise suppressor while retaining capability of functioning as a structural element.
Still another object of the present invention is to provide a jet engine housing constructed of a single sheet of the inventive acoustically and structurally functional porous sheet defined herein.
These and other object of the present invention will become apparent throughout the description thereof which now follows.